Conventionally, a polymer electrolyte fuel battery disclosed in Patent Document 1 has been proposed. This type of fuel battery is configured by a fuel battery stack formed by stacking power generation cells. Each of the power generation cells includes a membrane electrode assembly having an electrolyte membrane, an anode electrode layer, and a cathode electrode layer. The anode electrode layer is formed on a first surface of the electrolyte membrane and the cathode electrode layer is deposited on a second surface of the electrolyte membrane. Fuel gas such as hydrogen gas and oxidant gas such as air are supplied to the anode electrode layer and the cathode electrode layer through a gas flow passage forming member (a collector). This causes an electrode reaction in the membrane electrode assembly, thus generating power. The generated power is output to the exterior through the collector and a plate-like separator.
The gas flow passage forming member must be capable of efficiently supplying both of the fuel gas and the oxidant gas to the anode electrode layer and the cathode electrode layer. According to the configuration disclosed in Patent Document 1, the gas flow passage forming member is configured by a metal lath formed into a metal plate. A plurality of small through holes with predetermined shapes are formed in the metal lath. Also, substantially hexagonal through holes are formed in the metal lath in a mesh-like manner by machining a stainless steel plate with the thickness of approximately 0.1 mm into metal lath. Annular portions (strands) each forming the hexagonal through hole are connected together in a mutually overlapping state. Accordingly, the metal lath has a stepped cross section.
In the power generation cell, a carbon paper sheet formed of conductive fibers is arranged between the surface of each of the electrode layers and the gas flow passage forming member. The carbon paper sheets efficiently diffuse the fuel gas and the oxidant gas to the corresponding electrode layers. When the fuel battery stack is configured by stacking the multiple power generation cells, two separators, which are arranged in an upper portion and a lower portion of each power generation cell, are moved closer to each other in order to cause electric contact between the carbon paper sheets and the gas flow passage forming members. FIG. 49 illustrates a conventional gas flow passage forming member 1021 arranged between a carbon paper sheet 19 bonded to an anode electrode layer 17 and a separator 23. In this state, when the separator 23 is pressed downward, contact portions 1028 of the gas flow passage forming member 1021 are pressed firmly against the carbon paper sheet 19 and bite into the carbon paper sheet 19, as illustrated in FIG. 50.
Accordingly, the contact portions 1028 may cut a portion of the carbon paper sheet 19, thus deteriorating the function of the carbon paper sheet 19 as a gas diffusion layer. Also, a portion of the gas diffusion layer may enter the fuel gas flow passage in the gas flow passage forming member 1021, thus decreasing the effective area of the fuel gas flow passage. This increases pressure loss of the fuel gas, thus decreasing the supply amount of the fuel gas and lowering the power generation efficiency. Further, cut carbon fibers may be carried by the fuel gas and adhere to walls of the narrow gas flow passage in the gas flow passage forming member, thus clogging the passage. This hampers flow of the fuel gas and decreases the power generation efficiency. Also, the amount by which the contact portions 1028 bite into the carbon paper sheet 19 vary among power generation cells. This destabilizes the power generation voltage.
The gas flow passage forming member 1021 has contact portions 1030, which are arranged at the opposite side to the contact portions 1029a. Corners of the contact portions 1030 contact the separator 23, thus damaging the separator 23. Further, in this case, it is difficult to ensure a contact surface area necessary for current carrying between the gas flow passage forming member 1021 and the separator 23. This hampers supply of an electric current from the gas flow passage forming member 1021 to the separator 23, thus lowering the power generation efficiency.
To solve the above-described problem, a metal lath forming device illustrated in FIG. 40 has been employed. With reference to FIG. 40, the metal lath forming device includes a first shearing die 333 having a single shearing edge 333b and a second shearing die 334, which is arranged above the first shearing die 333 and has recesses 334b and projections 334a that are arranged alternately. When a metal lath is formed using the device, the recesses 334b and the projections 334a form upper semi-annular portions and lower semi-annular portions, respectively, in an alternating manner, through a single cycle of descent and ascent of the second shearing die 334. In this case, the lower semi-annular portions formed by the projections 334a are deformed downward so as to cause the upper semi-annular portions formed by the recesses 334b to sag diagonally downward. Each of such sagging portions forms a bent flat surface portion 1029a, as illustrated in FIG. 51. The bent flat surface portion 1029a functions as a contact portion 1029a of the gas flow passage forming member 1021 and is held in surface contact with the gas diffusion layer 19. In this manner, the aforementioned problems caused by biting of the contact portions 1029a are solved. However, since the bent flat surface portion 1029a is formed, the thickness T of the gas flow passage forming member 1021 decreases. This reduces the effective area of the gas flow passage and lowers the power generation efficiency.